Powder device with a constant supply of powder

ABSTRACT

A device for powder, wherein a powder container, an intermediate container and a dosing element are successively arranged in a versicle container. The powder is conveyed from the powder container into the intermediate container and, subsequently, into the dosing element. This results in a regular discharge.

DESCRIPTION

The invention concerns a powder device for powder coating printedsheets, with a powder container in which powder is stored and from whichpowder is taken, where the powder container in particular is designed asa replaceable container and can be removed from the powder device, andwith a metering mechanism by means of which a specified quantity ofpowder is dispensed into a current of air.

It is generally known that printed sheets of paper are powder coatedafter they leave the printing press so that the printing ink is notsmeared as the sheets are being stacked. To do this, a sheet deliverydevice has a powder device with which the powder is applied to thesheets.

Normally the powder devices have a powder container in which the powderis stored. This powder container has an opening at its lower end, whichis sealed, for example, by a ball (DE 38 11 309 A1). In order to be ableto take powder from the container, the ball is driven into the containerand thus into the powder stored in it, whereby the powder is loosenedup. In addition, compressed air is blown in when the container isopened. The powder taken from the container falls into a mixturepreparation area in which the compressed air is enriched with powder,and a powder-air mixture is created.

Another device provides for the discharge opening of the powdercontainer to be sealed by a moveable disk. When the disk is moved, aspecific quantity of powder trickles out of a gap between the disk andthe discharge opening of the powder container. This powder is picked upand carried along by a current of air rushing by. If the powdercontainer on this device is removed, for refilling, for example, the aircannot be enriched with powder. Continuous operation is not possible.

The object underlying the invention is to provide a powder device withwhich continuous operation is ensured even when the powder container isbeing replaced.

The object is achieved under the invention by having the powdercontainer empty into an intermediate container and positioning theintermediate container between the powder container and the meteringmechanism.

It is essential to the invention that the powder taken from the powdercontainer is not carried directly into the air stream but ends up in anintermediate container, from which the powder is fed through themetering mechanism into the air stream proper. The intermediatecontainer acts as an additional supply chamber, so that powder cancontinue to be taken from the intermediate container when, for example,the powder container is being replaced, whereby continuous operation isensured even when the powder container is (briefly) removed.

A further advantage can be seen in that the powder in the intermediatecontainer has a constant density as far as possible, independent ofwhether the powder was filled into the powder container only a shorttime previously and therefore still contains a relatively highpercentage of air, or whether the powder was filled into the powdercontainer a considerable time previously and has a higher density.

Since the powder from the powder container runs into the intermediatecontainer, and the time spent in the intermediate container isrelatively constant, the powder is transferred into the meteringmechanism with almost consistent density and consequently with an almostconstant percentage of air. In this way, the amount of powder in thecompressed air is adjusted even more precisely to the desired value.

A further embodiment provides that the powder container, theintermediate container and the metering mechanism are positionedvertically one above the other, and the powder is transferred downwardfrom one element to the next. In this way, the powder flows from thepowder container by way of the intermediate container to the meteringmechanism solely by means of gravity, and no transport air is required.This has the considerable advantage that the powder is not stirred upand that the individual elements do not have to be sealed, or only withconventional means, to atmosphere.

On one working example it is envisaged that the intermediate containeris essentially designed to be funnel shaped. This has the considerableadvantage that the powder can settle inside the intermediate container,that the air contained in the powder can escape, whereby the powderattains a homogenous density. The air is expelled from the powder bymeans of the gradual narrowing of the cross section of the intermediatecontainer.

An additional advantage of the invention can be seen in the intermediatecontainer having, at least partially, an elastic outer wall. By means ofthe elastic outer wall, which is made, for example, of plastic or rubberand is in turn also funnel-shaped, formation of bridges or pillarsinside the powder stored in the intermediate container is prevented.

Normally the powder container has a means of causing the powdercontainer to vibrate, for example, a vibrator or a drive to open andclose the discharge opening, and normally the metering mechanism alsocauses vibrations, which are transferred to the intermediate container.These vibrations create movement in the elastic container wall, so that,as a result of these vibrations, the powder is preventing from bakingonto the interior container wall. The elastic outer wall is positioneddirectly ahead of the metering mechanism. This is where the crosssection in the intermediate container is at its narrowest, and where therisk of bridging is greatest.

Consistent filling of the intermediate container is achieved under theinvention by the intermediate container having a sensor to register thefill level of the powder. If the level drops below a preset value,powder is taken from the powder container and the intermediate containeris replenished. The hysteresis between the sensor signal and thereplenishment can be set at any point. The advantage is that theintermediate container is always replenished when about 10% of thevolume of powder stored in it has been removed.

Under a preferred embodiment, the sensor is an optical sensor, aninductive sensor or a capacitative sensor. In the case of an opticalsensor, it can be designed as a light curtain, with visible or infra-redlight.

An additional advantage is also seen in designing the intermediatecontainer as an open system. Using an open system, removal of the powdercontainer is relatively unproblematic, since no provisions have to madefor seals or air closures. In addition, open systems of this kind can beproduced more economically than systems which are pressurized bycompressed air.

In order to allow the powder to drop to the bottom or settle in theintermediate container, the intermediate container is under atmosphericpressure.

Additional advantages, properties and details of the invention can beseen in the dependent claims and in the following description, in whicha particularly preferred working example is described in detail, withreference to the drawing. The properties shown in the drawing and namedin the claims and in the description can be essential to the inventionin each case individually or in any combination.

The drawing shows a lower section of powder container 1, which isattached in a container holder 2 by means of a quick-lock system 3. Thecontainer holder 2 swings perpendicular to the plane of the drawing. Thepowder container 1 has a discharge opening 5 at its lower end 4 for thepowder stored in the powder container 1. This discharge opening 5 opensinto an intermediate container identified in its entirety as 6, whichfor its part discharges into metering mechanism, identified in itsentirety as 7. This metering mechanism 7 is flexibly mounted above itsdrive. Between the underside of the container holder 2 and the upperside of the intermediate container 6 there is a gap 8, by which theinterior of the intermediate container 6 is connected to atmosphere.Atmospheric pressure therefore obtains in the intermediate container 6.The lower end 4 of the powder container 1 extends relatively far intothe intermediate container 6, which ensures that no or only a negligiblysmall amount of powder escapes through the gap 8. The gap 8 also has theadvantage that the intermediate container 6 is not attached to thecontainer holder 2 and therefore also separated from the vibratorymotion of the powder container 1.

The section 9 of the intermediate container 6 which faces the powdercontainer 1 has a cylindrical casing 10 at the top and a lowercylindrical casing section 11, which has a smaller diameter than thesection 10. The two casing sections 10 and 11 are joined by means of atapered casing section 12. An upper cylindrical casing section 14 of alower section 13 is pushed onto the open end of the lower casing section11. A tapered casing section 15, which terminates in a cylindrical lowercasing section 16, is attached to this casing section 14 in the sameway. This lower casing section 16 is attached to the metering mechanism7.

Section 13 of the intermediate container 6 consists of an elasticmaterial, for example, plastic or rubber, whereas section 9 is made of arigid material, for example, aluminum. Because the metering mechanism 7is switching on and off, particularly the drive for the meteringmechanism 7, vibrations are introduced into section 13. These vibrationsor motions respectively cause a deformation in the elastic wall ofsection 13, whereby the powder located in the intermediate container 6is loosened, or at least is prevented from baking on or forming pillarsand bridges. This ensures a flow or stream of powder in the direction ofthe lower outlet.

From the drawing it can also be seen that a sensor 17, in particular alight curtain 18, is provided in material section 11, by which the filllevel in the intermediate container 6 is determined. If the level fallsbelow a specified threshold value, a drive (not shown) is activated bymeans of the sensor 17, which acts in the direction of the arrow 19 on arocker, which is mounted to pivot around an axis 21. This causes aclosing mechanism 22 to be lifted from the discharge opening 5, andpowder can flow out of the powder container I into the intermediatecontainer 6. The powder, which is charged with air, is settled insidethe tapered casing section 15 and a uniform density is achieved. In thisway the discharge is evened out through the metering mechanism 7.

Additionally, the fill level is permanently maintained at the sameheight during operation, so that the fill level in the intermediatecontainer has no effect on the metering. The height of the level in thepowder container and the density of the powder in the powder containerhave no effect on the metering, because the powder container iscompletely separated from the metering process. This is because theintermediate container is positioned between the powder container andthe metering mechanism.

What is claimed is:
 1. A powder device to powder coat printed sheets,with a powder container, in which powder is stored and from which powderis taken, and with a metering mechanism, by means of which a specificquantity of powder is dispensed into a current of air, where the powdercontainer discharges into an intermediate container and the intermediatecontainer is located between the powder container and the meteringmechanism, characterized in that a discharge opening of the powdercontainer lies above a fill level in the intermediate container and thepowder container, the intermediate container and the metering mechanismare positioned vertically and sequentially one above the other, and thepowder is transferred from one to another downwardly.
 2. The powderdevice in accordance with claim 1, characterized in that theintermediate container is funnel shaped.
 3. The powder device inaccordance with claim 1, characterized in that the intermediatecontainer has at least a partially elastic wall.
 4. The powder device inaccordance with claim 2, characterized in that the elastic wall islocated immediately ahead of the metering mechanism.
 5. The powderdevice in accordance with claim 1, characterized in that theintermediate container has a sensor which indicates the fill level. 6.The powder device in accordance with claim 5, characterized in that thesensor is one of an optical sensor.
 7. The powder device in accordancewith claim 1, characterized in that the intermediate container isdesigned as an open system.
 8. The powder device in accordance withclaim 1, characterized in that atmospheric pressure is present in theintermediate container.
 9. The powder device in accordance with claim 1,characterized in that the powder container is designed as a replaceablecontainer and can be removed from the powder device.